In the distribution of gas, particularly gas that is used for fuel, an accidental break in the distribution line may have serious consequences if the flow of gas cannot be immediately interrupted. Such lines are usually buried in the ground and are not readily accessible for repair and maintenance purposes. It is therefore imperative to provide means for promptly interrupting the flow of gas in the line when a break occurs to prevent the escape of the gas and thereby avoid serious danger. Various types of valves have been provided for this purpose.
For example, U.S. Pat. No. 3,476,133 to Stedfield discloses a valve that operates automatically in response to a drastic change in pressure to interrupt the flow of gas in a distribution line. However, the valve is held in the open position by a shear pin or a shear disc which are sheared by a combination of the change in pressure plus the pressure applied by a spring. If, for any reason the shear pin or shear disc fail to shear as calculated, the valve will not function. Any change in the designed pressure by the spring may likewise cause a malfunctioning of the valve. Moreover, once the valve has been actuated it must be disassembled to restore it to the original position.
In like manner, U.S. Pat. No. 2,942,618 to Hodges provides an automatic valve for interrupting the flow of gas in a distribution line upon the occurrence of a drastic change in pressure in either direction. However, the structure depends upon a magnetic field to retain the valve in the open position. A change in the magnetic forces could cause the valve to malfunction. Moreover, the valve depends on a spring to respond to the change in pressure in the line. Any change in the physical properties of the spring could likewise result in the failure of the valve to operate properly. A further disadvantage lies in the fact that the valve must be manually reset which could present a problem if it were buried in the ground.
Finally, U.S. Pat. No. 2,785,698 to Vance discloses another construction in which the valve includes a diaphragm and a spring that respond to a change in pressure to actuate the valve. Any changes or miscalculation of the physical properties of the spring and diaphragm could cause a malfunctioning of the valve. Moreover, the open position is confined to a very narrow pressure range as determined by the spring weight and the diaphragm area. Also the Vance valve is not bidirectional.
Such reliance on physical structures as shear pins, shear discs, springs, diaphragms, or the like, is entirely eliminated in the present invention. Instead, the size of an aperture and a pressure storage chamber volume are the only major items that need be calculated for proper operation of the valve and, once established, specific behavior patterns may be readily maintained. In addition, the possibility of error in its manufacture is reduced to an absolute minimum and its accuracy of operation readily checked by a simple measurement. A further advantage lies in the fact that the valve requires very little, if any, maintenance and it will reset itself automatically upon the restoration of equal gas pressure on both sides of the valve.
It is accordingly, a general object of the present invention to provide an improved automatic gas shutoff valve that is simple and inexpensive to manufacture but which will operate with improved efficiency and greater reliability than the valves in the prior art.